Solenoid actuator assemblies are well known in the art for actuating pilot valves. Pilot valves are utilized to control fluid operated systems, for example, implements, transmissions, engine fuel injector systems, and the like. In applications where the position of the pilot valve is either open or closed and does not require accurate modulation a conventionally constructed solenoid actuator assembly of relatively primitive design is satisfactory. Such conventional solenoid actuator assemblies typically utilize component parts that have a large mass since controllability, dampening, responsiveness, and other such functional characteristics are not important. In some systems functional characteristics such as accuracy, smoothness, and responsiveness of control is extremely important. In such applications a proportional solenoid actuator assembly is more suitable.
A proportional solenoid actuator assembly has an output force which is proportional to the electrical current applied to the coil and is independent of the armature position over the range of the armature stroke. This proportionality allows for precise positioning of a pilot valve by selectively applying full or partial electrical current to the solenoid coil and thereby varying the output force. An example of a proportional solenoid actuator assembly is shown in United States Pat. No. 5,208,570 dated May 4, 1993 to Andrew H. Nippert, the inventor of this invention. Such solenoids have performed well, however, they tend to be difficult to manufacture and assemble.
The armature of proportional solenoid actuator assemblies also have mass which is greater in magnitude than that required to forcibly move the pilot control valve. As indicated above, any extra mass, affects the operating characteristics, however, the extra mass may be necessary to provide satisfactory operation based on other functional and structural design parameters.
The extra mass in some proportional actuator assemblies is included in the length of the armature in order to provide satisfactory sliding motion of the armature in the bore of the housing. Since surfaces of the armature and the bore of the housing define the axial sliding bearing surfaces of the armature, it is necessary to provide a bearing fit between the surface of the bore and the surface of the armature. This requires tight tolerances and smooth surfaces on the mating pieces. As a result, the time of manufacture is substantially increased and also the associated cost of manufacture.
In solenoid actuator assemblies having a combination of armature shaft slidably disposed in a sleeve bearing and the armature slidably disposed in the housing bore, as discussed above, axial alignment and concentricity between the spaced apart sleeve bearing and the housing bore is critical. Since the bore of the sleeve bearing and the bore defining the housing bearing are of different diameters the ability to maintain alignment and concentricity within acceptable tolerances is extremely difficult. Therefore, a substantial amount of rework and scrap is generated resulting in a further increase in the cost of the solenoid actuator assemblies.
Prior solenoid actuator assemblies used in fluid operated applications required the addition of axial passages in the armature to permit the flowing of fluid between opposite ends of the aperture in order to prevent a hydraulic locking of the armature. These passages also served to dampen armature movement and to improve armature stability. The addition of these apertures adds to the time and cost of manufacture of the solenoid actuator assembly.
State of the art actuator assemblies consist of a substantial number of piece parts which increases the amount of assembly time. Also, many of the piece parts are thin in crossection making it difficult to permanently connect them together by known processes such as welding, brazing, and the like without causing distortion.
The present invention is directed to overcoming one or more of the problems as set forth above.